Normally there is cycle of ups and downs in Property. But what happened in the recent past are mostly influenced by events (natural, social or political calamity) like 9/11, SARS. What we are going thru now is not a recession per say rather it is a global financial tsunami or a disaster or a deluge as u may wish 2 call it as. Moreover, Singapore Property Market may behave differently from others depending on supply of new units, general supply of units, improvements in certain estates and the sustenance of the gap between Private and Public Housing.

Based on statistics from 1960s to recently, drop in property market were all due to economic downturn.
1980s --> global economic recession, due to oil crisis
1998 --> Asian financial crisis
2001 --> Economic jitter due to September 11 attack on US soil
2003 --> SARS

Property price will always go up and down in tandem with economic performance.
If you predict Singapore economy will go down hill in 2 years time, then logically property market will go down as well.
But if Singapore economy continues to be bullish after 2 years, the property market will continue to climb (maybe not at the rate we saw in the past few months)

DECLINE, is too strong a word... we investors prefer the term 'market correction' hee hee :)